Recent wireless communication systems have been utilizing code division multiplexing (CDM) and orthogonal frequency division multiplexing (OFDM). For example, FIG. 12 shows an outline of a wireless communication system arranged with multiple base stations BS1, BS2 connected to a network (the network not pictured in the drawing) and a mobile station MS. The mobile station MS communicates with the base stations BS1, BS2 with a good reception condition depending upon the mobile station MS position. A CDM system is a multiplex system which spreads a frequency utilizing different spreading codes. CDM systems tend to suffer from a problem in that if the number of the spreading codes increases the peak power becomes larger than the average power. An OFDM system is a transmission system which transmits on multiple sub-carriers related with respect to orthogonal frequency position. OFDM systems tend to suffer from a problem in that if the sub-carrier's phase timing overlap the peak power becomes larger than the average power.
The base stations BS1, BS2 and mobile station MS have a composition that includes a reception processing unit that demodulates and decodes signals received by an antenna and a transmission processing unit that transmits encoded and modulated signals from an antenna, and the transmission processing unit has a transmission amplifier that amplifies signals of wireless frequency. This transmission amplifier has an amplification characteristic which includes linear and non-linear characteristics. If an input signal amplitude is large, the transmission amplifier amplifies the input signal in a non-linear characteristic area therefore, the amplified output signal of the amplifier includes distortion.
Proposals to deal with such problems have been shown by Japanese laid open application 2000-106548 which is known prior art in CDM systems.
Moreover, Japanese laid open application H11-205276 is known prior art in OFDM systems of multiple sub-carriers.
Regarding the CDM and OFDM systems, if the transmission amplifier is built so as to amplify up to the peak power without distortion, there will be a problem of increasing cost of the amplifier.
Possible solutions to the above problems include the idea to suppress the peak and improve the peak to average power ratio (PAPR) by applying a system that provides a dummy code for peak suppression as in the above-described conventional CDM system, or a system that provides a subcarrier for peak suppression as in the OFDM system. However because a dummy code or non-information signal for PAPR suppression has a problem that the data information transmission efficiency is decreased.